Infusion of fluid into the body or aspiration of fluid from the body is often performed with a catheter which is inserted beneath the skin. The catheter has a lumen through which fluid can flow. In some designs, the lumen is closed at the insertion end of the catheter and fluid communication between the body environment outside the catheter and the lumen is controlled by a slit through the catheter wall which acts as a valve. The catheter has a hub on the end outside the body which can be connected to a syringe for increasing and decreasing the pressure inside the lumen.
For infusion, the fluid pressure inside the lumen is increased to force the catheter body adjacent the slit to flex outward, separating the opposing faces of the slit and forming an aperture through which fluid may pass to the body environment. For aspiration, the pressure inside the lumen is decreased to force the catheter body adjacent the slit to collapse inward, forming an aperture through which fluid may flow into the lumen. At neutral pressures, the catheter body assumes an unflexed condition in which the faces of the slit are opposed, which forms a seal to prevent infusion or aspiration.
A valve can be made to permit infusion only, aspiration only, or both infusion and aspiration. A valve that operates for infusion only can be formed by making the slit in a convex catheter wall portion, since the convex shape facilitates flexing outward while resisting flexing inward. A valve that operates for aspiration only can be formed by making the slit in a concave wall portion, which facilitates flexing inward while resisting flexing outward. A flat wall portion facilitates flexing in either direction and can be used to form a two-direction valve.
A two-direction valve may also be formed by chemical weakening of the catheter wall adjacent the slit, which facilitates flexing in both directions so that the valve works smoothly during infusion and aspiration. The lumen may also be shaped with a linear side that terminates to form regions of reduced catheter wall thickness. The regions act as hinges at which inward and outward flexing is enhanced and the area between the regions may have a greater wall thickness which facilitates sealing.
The catheter may also have multiple valves and multiple lumens. Further discussion of catheters is found, for example, in Groshong U.S. Pat. No. 4,549,879, Nichols U.S. Pat. No. 4,753,640, Lui U.S. Pat. No. 5,261,885, and Luther U.S. Pat. No. 5,522,807 the entire contents of all of which are incorporated herein by reference.